Method, apparatus and system for visual gamma correction of displays

ABSTRACT

A method, apparatus and system for visual gamma correction of a display system includes retrieving input gamma information from input content, determining at least one pattern representing luminance of the received content based upon at least the retrieved gamma information, displaying the at least one determined pattern representing the luminance of the received image content and at least one corresponding reference image on the display system, and adjusting the brightness and contrast of the least one reference image on the display system to approach the luminance of a corresponding determined pattern to determine a corrected gamma for the display system.

This application claims the benefit, under 35 U.S.C. §365 of

International Application PCT/US2006/047762, filed Dec. 14, 2006, whichwas published in accordance with PCT Article 21(2) on Jun. 19, 2008 inEnglish.

TECHNICAL FIELD

The present invention generally relates to display calibration andcharacterization, and more particularly, to visual gamma correction of adisplay such that the display can more accurately display gammacorrected video sequences or images.

BACKGROUND OF THE INVENTION

Gamma correction provides for an accurately depicted display image on adisplay device. More specifically, Gamma correction controls the overallbrightness of an image. Images which are not properly corrected mayappear bleached out, or too dark. Gamma correction affects not only thebrightness, however, but also the ratios of red to green to blue. Gammacorrection is applied to a voltage response curve used to render imagesin various instances to compensate for differences in intensity. Thatis, a range of voltages sent to a display can generally be less than thedesired or required voltages for correct display of an image. As such,the voltages require correction to more accurately depict the image.Since the relationship between the voltage sent to the display and theintensity which the display produces are known, a signal can becorrected by gamma correction before it gets to the display.

In conventional systems, input source images have associated with themassumed gamma characteristics for a display (e.g., Rec. 709 gamma, whichis a transfer function known in the art). However, most displays depictdifferent gamma characteristics from those assumed, such that inputimages are not correctly depicted on the display. A conventional methodof characterizing a display includes measuring patches on the displayusing, for example, a spectroradiometer. In particular, for gammacharacteristics, a series of patches are measured (this is called aramp—e.g., a gray ramp is (Red, Green, Blue)=(0,0,0), (32,32,32), (64,64, 64), . . . , (224, 224, 224), (255, 255, 255)). After themeasurement, a gamma curve can be plotted (e.g., luminance vs. digitalvalue). FIG. 1 depicts an illustrative plot of luminance versus inputdigital value for use in gamma correction of an image.

The gamma curve 10 of FIG. 1 is typically implemented to compensate forincorrect input gamma values.

Digital video capture images or still capture images are gamma correctedby assuming certain gamma characteristics for display systems. Forexample, for high definition (HD) displays, Rec. 709 gamma is appliedfor gamma correction of an input device or input images. For displayingimages that look-like film images on a display, a proprietary gamma(either a gamma power function curve or lookup table (LUT)) is appliedfor the gamma correction. However, the gamma characteristic of thedisplays usually does not match the assumed gamma correction applied forthe input space. As such, in a typical characterization method, theinput gamma is linearized (inverse gamma correction) and the gamma iscorrected again using the display gamma.

FIG. 2 depicts an exemplary flow diagram of a conventional method forgamma correction along with corresponding plots of luminance versusinput digital value for each of the steps of the flow diagram. Themethod of FIG. 2 begins in block 20, in which input gamma is determinedfrom a received image. In block 22, the input is linearized by providinga LUT or function that linearizes the input gamma. Subsequently, inblock 24, the gamma changes attributable to displaying the receivedimage on the display are determined and corrected for, in block 26, toprovide a display gamma curve or function as depicted in FIG. 1. Plots30, 32, 34 and 36 of FIG. 2 illustratively depict the processingperformed by the corresponding process in blocks 20, 22, 24, and 26,respectively. Plots 30, 32, 34 and 36 illustrate a normalized luminance(y-axis) versus an input digital value (x-axis). Consistent with FIG. 2,a characterization of a display is performed to determine a moreaccurate representation of input images on the display.

While this methodology is accurate and reliable, it has some significantdrawbacks. For example, this method: 1) requires costly instrumentationto perform measurements; 2) requires time consuming methods to measure aplurality of patches; and 3) needs to derive the gamma curve frommeasurement data, among other things.

SUMMARY OF THE INVENTION

A method, apparatus and system in accordance with various embodiments ofthe present invention addresses the deficiencies of the prior art byproviding visual characterization of an output gamma using brightnessand/or contrast level controls of a display so that the display gammamatches an input source gamma.

In one embodiment of the present invention, a method for visual gammacorrection of a display system includes retrieving input gammainformation from input content, determining at least one patternrepresenting luminance of the received content based upon at least theretrieved gamma information, displaying the at least one determinedpattern representing the luminance of the received image content and atleast one corresponding reference image on the display system, andadjusting the brightness and contrast of the at least one referenceimage on the display system to approach the luminance of a correspondingdetermined pattern to determine a corrected gamma for the displaysystem. In various embodiments of the present invention, the at leastone pattern includes a halftone matrix having black and white dots wherea ratio of black and white dots is determined based on luminance of thereceived content. In addition, the at least one reference image caninclude a corresponding continuous-tone image for each of the determinedat least one patterns.

In an alternate embodiment of the present invention, an apparatus forvisual gamma correction of a display system includes a memory forstoring at least gamma information and control programs and a processorfor executing the control programs. The apparatus is configured toretrieve gamma information relating to received image content, determineat least one pattern representing the luminance of the received imagecontent based upon at least the received gamma information, enable thedisplay of the at least one determined pattern representing theluminance of the received image content and at least one correspondingreference image on the display system, enable the adjustment ofbrightness and contrast of the at least one reference image on thedisplay system to approach the luminance of a corresponding determinedpattern. In one embodiment of the invention, the apparatus generates agraphical user interface for enabling the display of the at least onedetermined pattern and the at least one corresponding reference image onthe display system for enabling the adjustment of the brightness andcontrast of the at least one reference image on the display system toapproach the luminance of a corresponding determined pattern.

In an alternate embodiment of the present invention, a system for visualgamma correction of a display system includes a content source forproviding image content and gamma information relating to the imagecontent, a video playback device for receiving the image content and thegamma information from the content source and for communicating displayimages to the display system, and a display system for displaying theimages communicated from the playback device. The system furtherincludes a gamma correction device including a memory for storing atleast the gamma information and control programs and a processor forexecuting the control programs. The gamma correction device of thesystem of the embodiment of the present invention is configured toretrieve the gamma information relating to the received image content,determine at least one pattern representing luminance of the receivedimage content based upon at least the retrieved gamma information,enable the display of the at least one determined pattern representingthe luminance of the received image content and at least onecorresponding reference image on the display system, and enable theadjustment of brightness and contrast of the at least one referenceimage on the display system to approach the luminance of a correspondingdetermined pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

The teachings of the present invention can be readily understood byconsidering the following detailed description in conjunction with theaccompanying drawings, in which:

FIG. 1 depicts an illustrative plot of luminance versus input digitalvalue for use in gamma correction of an image;

FIG. 2 depicts an exemplary flow diagram of a conventional method forgamma correction and corresponding plots of luminance versus inputdigital value for each of the step of the flow diagram;

FIG. 3 depicts a high level block diagram of a characterization systemfor determining gamma correction in accordance with an embodiment of thepresent invention;

FIG. 4 depicts a high level block diagram of an embodiment of a gammacorrection device suitable for use in the visual characterization systemof FIG. 3 in accordance with the present invention;

FIG. 5 illustratively depicts four different illustrative patternwindows in an exemplary gamma correction window in accordance with anembodiment of the present invention;

FIG. 6 depicts a graphical representation of a halftone image and acorresponding matrix used to generate the halftone image; and

FIG. 7 depicts a flow diagram of a method for characterizing/correctingdisplay gamma in accordance with an embodiment of the present invention.

It should be understood that the drawings are for purposes ofillustrating the concepts of the invention and are not necessarily theonly possible configuration for illustrating the invention. Tofacilitate understanding, identical reference numerals have been used,where possible, to designate identical elements that are common to thefigures.

DETAILED DESCRIPTION OF THE INVENTION

The present invention advantageously provides a method, apparatus andsystem for visual gamma correction. Although the present invention willbe described primarily within the context of a playback system and aplayback device using a single gamma curve, the specific embodiments ofthe present invention should not be treated as limiting the scope of theinvention. It will be appreciated by those skilled in the art andinformed by the teachings of the present invention that the concepts ofthe present invention can be advantageously applied in film colorcorrection, digital photography or any other application in which animage is rendered and applying one or more gamma curves.

The functions of the various elements shown in the figures can beprovided through the use of dedicated hardware as well as hardwarecapable of executing software in association with appropriate software.When provided by a processor, the functions can be provided by a singlededicated processor, by a single shared processor, or by a plurality ofindividual processors, some of which can be shared. Moreover, explicituse of the term “processor” or “controller” should not be construed torefer exclusively to hardware capable of executing software, and canimplicitly include, without limitation, digital signal processor (“DSP”)hardware, read-only memory (“ROM”) for storing software, random accessmemory (“RAM”), and non-volatile storage. Moreover, all statementsherein reciting principles, aspects, and embodiments of the invention,as well as specific examples thereof, are intended to encompass bothstructural and functional equivalents thereof. Additionally, it isintended that such equivalents include both currently known equivalentsas well as equivalents developed in the future (i.e., any elementsdeveloped that perform the same function, regardless of structure).

Thus, for example, it will be appreciated by those skilled in the artthat the block diagrams presented herein represent conceptual views ofillustrative system components and/or circuitry embodying the principlesof the invention. Similarly, it will be appreciated that any flowcharts, flow diagrams, state transition diagrams, pseudocode, and thelike represent various processes which may be substantially representedin computer readable media and so executed by a computer or processor,whether or not such computer or processor is explicitly shown.

In accordance with various embodiments of the present invention, aplurality of gamma curves can be implemented for gamma correction (e.g.,one or more gamma curve for each of three channels; red, green, blue).However, for simplicity, various concepts of the present invention willbe explained with reference to a single channel or color componentsignal and a respective gamma curve.

FIG. 3 depicts a high level block diagram of a visual characterizationsystem for determining gamma correction in accordance with an embodimentof the present invention. The visual characterization system 300 of FIG.3 illustratively comprises a content source 302, a playback device 306and a display device 308. In FIG. 3, the playback device 306illustratively comprises a gamma correction device 307. Although in thevisual characterization system 300 of FIG. 3, the gamma correctiondevice 307 is depicted as being integrated into the playback device 306,in alternate embodiments of the present invention, the gamma correctiondevice 307 can comprise a separate stand-alone component.

FIG. 4 depicts a high level block diagram of an embodiment of a gammacorrection device 307 suitable for use in the visual characterizationsystem 300 of FIG. 3 in accordance with the present invention. The gammacorrection device 307 of FIG. 4 comprises a processor 410 as well as amemory 420 for storing control programs, algorithms, gamma information,gamma patterns and the like. The processor 410 cooperates withconventional support circuitry 430 such as power supplies, clockcircuits, cache memory and the like as well as circuits that assist inexecuting the software routines stored in the memory 420. As such, it iscontemplated that some of the process steps discussed herein as softwareprocesses may be implemented within hardware, for example, as circuitrythat cooperates with the processor 410 to perform various steps. Thegamma correction device 307 also contains input-output circuitry 440that forms an interface between the various respective functionalelements communicating with the gamma correction device 307.

Although the gamma correction device 307 of FIG. 4 is depicted as ageneral purpose computer that is programmed to perform various controlfunctions in accordance with the present invention, the invention can beimplemented in hardware, for example, as an application specifiedintegrated circuit (ASIC). As such, the process steps described hereinare intended to be broadly interpreted as being equivalently performedby software, hardware, or a combination thereof.

In the visual characterization system 300 of FIG. 3, gamma informationof received image content from the content source 302 is determined.That is, image content 304 from the content source 302 can includeembedded gamma information or gamma information on a separate stream forthe image content in the form of, for example, metadata. In variousembodiments of the present invention, the content source 302 can includea compact disk (CD), a digital video disk (DVD), a floppy disk, a videostream or any other source of image information. As depicted in thevisual characterization system 300 of FIG. 3, the image content 304 fromthe content source 302 is received by the playback device 306.

The playback device 306 can include a DVD player, CD player, MP3 player,a set-top box, a personal computer or any other device suitablyconfigured to receive and process for display, the image content 304. Aspreviously recited, the image content 304 can include metadata storing agamma setting, curve or function identifying the gamma of the imagecontent 304. The gamma correction device 307 of the playback device 306of FIG. 3 determines a pattern to represent the luminance of the imagecontent 304 based upon the received gamma information of the imagecontent 304. For example, in one embodiment of the present invention,the gamma correction device 307 determines respective dot patterns(e.g., halftones) representing the gamma of the image content 304. Thepatterns representing the gamma of the image content 304 determined bythe gamma correction device 307 are displayed on the display 308 and arevisually compared to a continuous image also displayed on the display308. For example, in one embodiment, the continuous image displayed canbe a portion of the received image content 304. In an alternateembodiment of the present invention, the continuous image can be acontinuous-tone image in a single gray level generated by the gammacorrection device, where the gray-level of the continuous image can beadjusted for comparison to respective determined patterns representingthe gamma of the image content 304. The brightness and/or contrast levelof the display 308 are then adjusted such that an output gamma of thecontinuous image displayed on the display 308 matches the gamma of theimage content 304 as represented by the determined patterns.

For example, in one illustrative embodiment, the image content 304 isreceived by the playback device 306 (e.g. set-top box or proprietaryprocessing box) and prepared for display on the display 308. To ensureproper display of the image content 304, the playback device 306 via,for example the gamma correction device 307, determines if the gamma ofthe display 308 has been calibrated in accordance with the presentinvention. In one embodiment of the present invention, the gammacorrection device 307 maintains a list of previously calibrated displaysand determines by examining the stored list and by identification of aconnected display, if a connected display has been previouslycalibrated. In an alternate embodiment of the present invention, thegamma correction device 307 communicates with the display 308 todetermine if the connected display 308 has been previously calibrated.

If it is determined that the display 308 has not been calibrated,calibration of the gamma of the display in accordance with the presentinvention is initiated. As previously recited, the playback device 306receives the image content 304 along with metadata identifying the gammacharacteristics of the image content 304. The gamma correction device307 of the playback device 306 then determines a pattern(s) to representthe luminance of the image content 304 based upon the received gammainformation of the image content 304. The determined gamma pattern(s) isthen communicated to the display 308. In one embodiment of the presentinvention, the gamma correction device 307 can generate and communicateto the display 308 a control signal to cause the display 308 to enterinto a gamma correction mode. For example, the control signal generatedby the gamma correction device can cause the brightness and contrastcontrol mechanisms (e.g., scroll bars) of the display 308 to be madeavailable. Furthermore, the control signal can cause a gamma correctionwindow to be displayed on the display 308 for use in correcting thegamma of the display in accordance with the present invention.

For example, FIG. 5 illustratively depicts four different illustrativepattern windows P1-P4 in an exemplary gamma correction window/graphicalinterface 502 in accordance with an embodiment of the present invention.The correction window 502 can be generated by the display 308, by thegamma correction device 307 or a combination of both depending on thesystem configuration. In the embodiment of FIG. 5, each of the fourwindows P1-P4 of the gamma correction window 502 is further divided intotwo image windows. A top image window 504 includes a continuous-toneimage (as described above), and a bottom image window 506 includes apattern to represent the luminance of the image content 304 (e.g., ahalftone image) in accordance with the present invention. In theembodiment of FIG. 5, the continuous-tone images are images each havinga different grey scale value. The continuous-tone image of the topwindow 504 varies in gamma according to a control value of thebrightness and contrast level as set by, for example, the brightness andcontrast control mechanisms 510 and 512 of the display device 307. Forexample, in an 8-bit embodiment of the present invention, the brightnessand contrast range is 0-255; however, other bit resolutions can beemployed in accordance with the present invention.

In one embodiment of the present invention, a halftone image forrepresenting the gamma of the input image content includes black andwhite dots. The number of dots in the white background determines theoverall luminance. The computation of the luminance of checkerboardpattern where 50% of the dots are black can be characterized accordingto equation one (1) which follows:

$\begin{matrix}{{L_{H} = \left( \frac{L_{\max} + L_{\min}}{2} \right)},} & (1)\end{matrix}$

where L_(H) depicts the luminance of the checkerboard pattern, L_(max)depicts the luminance of the maximum gray level patch (white), andL_(min) depicts the luminance of the minimum gray level patch (black).If normalized luminance is used, then L_(max) is 1.0 and L_(min) isclose to 0.0, hence L_(H) is 0.5.

A gamma value may be determined by the relationship between theluminance and input digital values according to equation two (2) whichfollows:L=(D/255)^(γ),   (2)

where L depicts the luminance value and D depicts the digital value. The255 of equation two is based upon 8-bit resolution. Therefore, if gamma(γ) is known, for a given D value, a corresponding L value can becomputed. Once L is determined, by substituting L with L_(H) in Equation(1), the number of white and black dots can be specified for thehalftone image to represent the needed L value.

For example, pattern (P1) in FIG. 5 includes the halftone calculatedusing an input gamma (γ) and the given D value. Patterns P2, P3 and P4can be set in a similar way. The four patterns P1-P4 of FIG. 5correspond to four different D values (e.g., 50, 100, 150, and 200,respectively). It should be understood that although only one pattern isimplemented for the gamma characterization and correction in FIG. 5, inalternate embodiments of the present invention, a plurality of patternscan be implemented to improve the characterization and correctionaccuracy by providing a plurality of different reference points.

In the exemplary patterns P1-P4 in FIG. 5, γ=2.2 and D=100, 164, 186,224, respectively for P1-P4. Using these values and Equations (1) and(2), the first halftone for P1 should have 8 white dots and 56 blackdots in 8×8 array image determined as follows:

-   1. from Eq. (2), L=(100/255)^(2.2)=0.1275-   2. in Eq. (1), set L_(H)=L-   3. then from Eq. (1), 8 white dots are needed to make    L_(H)=(8*1.0+0.0)/64=0.125, which is close to the value L (0.1275).    Note that the denominator, (64), has been updated with the number of    positions in the 8×8 matrix. The halftone pattern would then    preferably include a repeating pattern to evenly distribute the    white dots with the black dots.

FIG. 6 depicts a graphical representation of a halftone image and acorresponding matrix used to generate the halftone image. For example,the halftone image of FIG. 6 illustratively comprises a repeated 8×8halftone array as described above for the halftone of P1. The halftoneimage 602 of FIG. 6 depicts how the determined white and black dots canbe arranged. The other halftone images in the windows P2-P4 aresimilarly determined using corresponding D and γ values. Halftone imagescan be generated using a digital pattern of highs and lows (1's and 0's)as shown in matrix 604 of FIG. 6 in which black is represented by a zero(0) and white is represented by a one (1). Once the halftone images aredetermined, each image can be displayed together with thecontinuous-tone images (as depicted in FIG. 5).

Referring back to FIG. 5, once the halftone images are determined anddisplayed together with the continuous-tone images on, for example, thegamma correction window/graphical interface 502 of FIG. 5, a user canadjust the brightness and/or contrast of the continuous-tone imagesusing, for example, the brightness and contrast control mechanisms 510and 512. That is, in accordance with an embodiment of the presentinvention, the brightness and contrast of the continuous-tone images on,for example, the gamma correction window/graphical interface 502 of FIG.5 are adjusted to achieve a best possible match between thecontinuous-tone images (504) and the respective halftone images (506).In the present invention, the halftone images are fixed and are notvaried with the respective continuous-tone images varied, for example,using the brightness and contrast control mechanisms 510 and 512. Assuch, an appropriate level of brightness and/or contrast of a displayare determined in accordance with the present invention such that theoverall gamma of the display closely matches the gamma of the inputimage content.

Several advantages of the concepts of the embodiments of the presentinvention presented herein include characterization/gamma correctionwithout the need for any specialized measurement instrumentation and thedisplay gamma can be tailored to the gamma of input image content, whichprovides an easier and more efficient means of gammacharacterization/correction. In addition, in accordance with the presentinvention, a user can subjectively decide on a best setting according topersonal preference.

Although in the embodiments of the invention described above, it wasassumed that gamma curves for the various channels of the input imagecontent (e.g., three channels; red, green, blue) are the same or verysimilar because the characterization/gamma correction was conducted ongray continuous-tone/halftone patterns, in alternate embodiments of theinvention, for the displays having different gamma curves for differentchannels, the concepts of the present invention can be extended to eachcolor pattern (e.g., R, G, B), and each of the respective gammas can becharacterized/corrected individually in accordance with the presentinvention.

In addition, although in the embodiments described above a powerfunction (e.g., Eq. (2)) was used to create a pattern representing thegamma of input image content, in alternate embodiments the gamma of theimage content may not be capable of being represented by a powerfunction. For example, if the gamma of the input image content isrepresented by an S-curve or another non-linear shape that was differentfrom the power function, some accuracy in the gammacharacterization/correction of the present invention can be lost.However, in accordance with the present invention, the loss in accuracycan be compensated by, for example, providing more patterns representingthe gamma of the input image content and as such, providing more grayscale images in the display for comparison to the patterns representingthe gamma of the input image content. In addition, gain and offset termscan be considered, for example, in Eq. (2). Gain and offset parameterscan be included as in the typical gamma characterizations.

FIG. 7 depicts a flow diagram 700 of a method forcharacterizing/correcting display gamma in accordance with an embodimentof the present invention. The method 700 of FIG. 7 begins at step 702 inwhich image content is received. The method 700 proceeds to step 704.

At step 704, gamma information of the input image content is retrieved.For example and as described above, in one embodiment of the presentinvention, image content 304 from the content source 302 can includeembedded gamma information or gamma information can be received on aseparate stream for the image content in the form of, for example,metadata. The method 700 proceeds to step 706.

At step 706, at least one pattern is determined to represent luminancebased upon the input gamma information and input digital values (see,e.g., Eqs. 1 and 2 as illustratively described above) of the input imagecontent. For example, in one embodiment of the present invention, thiscan include computing a halftone matrix having black and white dots. Aratio of black and white dots is determined based on luminance, and thematrix includes a spacing pattern between the black and white dots. Theplurality of dot patterns can correspond to a plurality of discreteinput digital values. The method 700 then proceeds to step 708.

At step 708, a corresponding continuous-tone image is generated for eachof the patterns determined in step 706. That is, in one embodiment ofthe present invention, a corresponding continuous-tone image can begenerated for a luminance level represented by each of the patternsdetermined in step 706. The method 700 then proceeds to step 710.

At step 710, the determined pattern(s) and the generated continuous-toneimage(s) are displayed on a display to be characterized/corrected inaccordance with the present invention. The method 700 then proceeds tostep 712.

At step 712, brightness and contrast are adjusted on the display toattempt to match the continuous-tone image(s) to the corresponding dotpattern(s) to correct the gamma settings of the display. The method 700is then exited.

As previously described, although the embodiment described in the method700 of FIG. 7, continuous-tone image(s) are generated for comparisonwith the determined pattern(s) (e.g., the dot patterns), in alternateembodiments of the present invention, the dot pattern(s) can instead becompared with an actual picture image displayed on the display. Inaddition and as previously described, although in the method 700 of FIG.7, the characterization/gamma correction was performed for a singlechannel or channels having substantially similar gamma curves, inalternate embodiments of the invention, the concepts of the presentinvention can be extended to a plurality of channels (e.g., R, G, B),and each of the respective gammas can be characterized/correctedindividually in accordance with the present invention.

Having described preferred embodiments for a method, apparatus andsystem for visual gamma correction in display systems (which areintended to be illustrative and not limiting), it is noted thatmodifications and variations can be made by persons skilled in the artin light of the above teachings. It is therefore to be understood thatchanges may be made in the particular embodiments of the inventiondisclosed which are within the scope and spirit of the invention asoutlined by the appended claims. While the forgoing is directed tovarious embodiments of the present invention, other and furtherembodiments of the invention may be devised without departing from thebasic scope thereof.

1. A method for visual gamma correction of a display system, comprising:retrieving gamma information relating to received image content;determining at least one pattern representing luminance of the receivedimage content based upon at least the retrieved gamma information;displaying the at least one determined pattern representing theluminance of the received image content and at least one correspondingreference image on the display system; and adjusting brightness andcontrast of the at least one reference image on the display system toapproach the luminance of a corresponding determined pattern.
 2. Themethod of claim 1, wherein the brightness and contrast of the at leastone reference image is adjusted to approach the luminance of acorresponding determined pattern to determine a corrected gamma for thedisplay system.
 3. The method of claim 1, wherein determining a patternincludes computing a halftone matrix having black and white dots.
 4. Themethod of claim 3, wherein a ratio of black and white dots is determinedbased on luminance.
 5. The method of claim 1, wherein digital values ofthe received image content are additionally used to determine the atleast one pattern representing the luminance of the received imagecontent.
 6. The method of claim 1, wherein a plurality of patterns aregenerated corresponding to discrete digital values of the received imagecontent.
 7. The method of claim 1, wherein the at least onecorresponding reference image comprises a continuous-tone image.
 8. Themethod of claim 1, wherein the reference image comprises an image ofsaid received image content.
 9. The method of claim 1, wherein a patternrepresenting the luminance of the received image content is determinedfor a plurality of channels.
 10. The method of claim 9, wherein theplurality of channels include color components of the received imagecontent.
 11. The method of claim 10, wherein the color componentscomprise red, blue and green color components.
 12. An apparatus forvisual gamma correction of a display system, comprising: a memory forstoring at least gamma information and control programs and a processorfor executing the control programs, the apparatus configured to:retrieving gamma information relating to received image content;determine at least one pattern representing luminance of the receivedimage content based upon at least the retrieved gamma information;enable the display of the at least one determined pattern representingthe luminance of the received image content and at least onecorresponding reference image on the display system; and enable theadjustment of brightness and contrast of the at least one referenceimage on the display system to approach the luminance of a correspondingdetermined pattern.
 13. The apparatus of claim 12, wherein the apparatusgenerates a graphical user interface for enabling the display of the atleast one determined pattern and the at least one correspondingreference image on the display system for enabling the adjustment of thebrightness and contrast of the at least one reference image on thedisplay system to approach the luminance of a corresponding determinedpattern.
 14. The apparatus of claim 12, wherein said apparatus is acomponent of a video playback device.
 15. The apparatus of claim 12,wherein the at least one pattern comprises at least one halftone matrix.16. The apparatus of claim 12, wherein a plurality of dot patterns aregenerated corresponding to discrete digital values of the received imagecontent and wherein the at least one reference image comprises acorresponding continuous-tone image for each of the plurality of dotpatterns, the continuous-tone images being adjustable by the brightnessand contrast controls of the display system to approach the luminance ofa corresponding determined pattern to determine a corrected gamma forthe display system.
 17. The apparatus of claim 12, wherein digitalvalues of the received image content are additionally used to determinethe at least one pattern representing the luminance of the receivedimage content.
 18. The apparatus of claim 12, wherein the at least onecorresponding reference image is generated by the apparatus.
 19. Asystem for visual gamma correction of a display system, comprising: acontent source for providing image content and gamma informationrelating to the image content; a video playback device for receiving theimage content and the gamma information from the content source and forcommunicating display images to the display system; the display systemfor displaying the images communicated from the playback device; and agamma correction device including a memory for storing at least thegamma information and control programs and a processor for executing thecontrol programs, the gamma correction device configured to: retrievethe gamma information relating to the received image content; determineat least one pattern representing luminance of the received imagecontent based upon at least the retrieved gamma information; enable thedisplay of the at least one determined pattern representing theluminance of the received image content and at least one correspondingreference image on the display system; and enable the adjustment ofbrightness and contrast of the at least one reference image on thedisplay system to approach the luminance of a corresponding determinedpattern.
 20. The system of claim 19, wherein the gamma correction devicegenerates a graphical user interface for enabling the display of the atleast one determined pattern and the at least one correspondingreference image on the display system for enabling the adjustment of thebrightness and contrast of the at least one reference image on thedisplay system to approach the luminance of a corresponding determinedpattern.
 21. The system of claim 20, wherein the graphical userinterface is displayed on the display system.
 22. The system of claim19, wherein the display system comprises brightness and contrastcontrols configured to adjust the brightness and contrast of the atleast one reference image on the display system to approach theluminance of a corresponding determined pattern to determine a correctedgamma for the display system.
 23. The system of claim 19, wherein thegamma correction device is integrated in the video playback device. 24.The system of claim 19, wherein digital values of the received imagecontent are additionally used to determine the at least one patternrepresenting the luminance of the received image content.
 25. The systemof claim 19, wherein the at least one corresponding reference image isgenerated by the gamma correction device.